In a rolling mill for flat products having work rolls driven by electric motors and backup rolls supporting the rolling reaction force applied to the work rolls, the method has been employed of shifting the work roll axial center positions and backup roll axial center positions to give a certain length of rolling direction offset and generating a horizontal direction (unless particularly stated to the contrary, the “horizontal direction” indicates the rolling direction) force component of the rolling reaction force to push the work rolls and thereby roll flat products of stable shapes. Various proposals have been made in the past.
For example, Japanese Patent No. 2796465 discloses a cross roll rolling milling of a structure pushing the work roll chocks in the horizontal direction.
However, the rolling mill of this Japanese Patent No. 2796465 is of a structure pushing only the work roll chocks, so there was the problem that it was not possible to suppress fluctuation in the amount of work roll offset due to looseness of the work roll bearings present between the work roll chocks and the work rolls.
Japanese Patent No. 2972401 discloses a rolling mill for flat products providing support rollers for supporting the work rolls in the horizontal direction at the entrance and exit sides of the rolling mill.
The work rolls of the rolling mill of this Japanese Patent No. 2972401 assume small sized work rolls for rolling hard materials and ultrathin materials. They are not directly driven by electric motors, but are indirectly driven through the backup rolls. In the case of indirect drive, due to the transmission of the drive force, a large horizontal force acts on the work rolls from the backup rolls. Due to the interaction with the horizontal direction force of the rolling load, this becomes a cause of instability. In particular, in the case of small sized work rolls, the horizontal direction deflection of the work rolls becomes large whereby this instability is aggravated, so it was necessary that both smaller size of the work rolls and increase of the rigidity be achieved by the horizontal direction support rollers.
However, this rolling mill is designed for elimination of deflection and minimization of the size of the work rolls by greatly increasing the rigidity of the small sized work rolls, so the problems of zero point adjustment used as the standard in control of rolling and maintenance of the zero point adjustment state are not solved.
Japanese Patent No. 2885102 discloses a rolling mill for flat products providing support rollers for support in the horizontal direction at one sides of the work rolls.
However, the rolling mill of this Japanese Patent No. 2885102, like the rolling mill of Japanese Patent No. 2972401, is a rolling mill of an indirect drive type using small sized work rolls. In the same way as Japanese Patent No. 2972401, due to the small sized rolls, the roll rigidity is small and deflection in the horizontal direction easily occurs. If a difference in deflection occurs between the upper and lower work rolls, the rolling becomes instable, so to increase the work roll rigidity in the horizontal direction and control the system so that no difference in deflection occurs between the upper and lower work rolls, horizontal direction support rollers are provided at the upper and lower work rolls.
The support rollers used in this rolling mill are structured to support the work rolls by giving forces in a direction opposite to the horizontal direction force component of the rolling reaction force generated due to offset of the work rolls, so were not able to stabilize the axial center positions of the work rolls. Further, in the same way as the work rolls of Japanese Patent No. 2972401, the problems of zero point adjustment used as the standard in control of rolling and maintenance of the zero point adjustment state are not solved.
Japanese Patent No. 2966172 discloses a rolling mill for flat products providing intermediate rolls for giving horizontal direction deflection at one side or both sides of the work rolls. This positively applies deflection to the work rolls so as to control the shape of the rolling material by the profiles of the work rolls (in particular the surface relief in the pass line direction of the rolled material). For this reason, the intermediate rolls are structured tapered. The work rolls are made to deflect along this, so a bending force is given to the bearings.
However, the axial ends of the work rolls used in the rolling mills of this Japanese Patent No. 2966172 are structured to give the horizontal direction bending force for support in load control. There was the problem that the structures did not strictly control the work roll offset positions. Further, the problems of zero point adjustment and maintenance of the zero point adjustment state, that is, the inability to determine the reference points in rolling control, remained.
Japanese Patent Publication (A) No. 10-277619 discloses a rolling mill for flat products imparting a horizontal force to one of the upper and lower work rolls.
The rolling mill of this Japanese Patent Publication (A) No. 10-277619 is a rolling mill in which the axial centers of the work rolls are offset from the axial centers of the backup rolls in the rolling exit side direction wherein when the rolled material leaves the rolling mill, the upper and lower work rolls contact if the roll gap is small and the difference in size of the upper and lower work rolls will cause the large sized roll to move in the rolling entrance direction, so to prevent this, a horizontal force imparting device is set at the large sized side roll and the large sized work roll is pushed in the rolling exit side direction.
However, the horizontal force is given by the invention of Japanese Patent Publication (A) No. 10-277619 assuming application to only the large sized work roll when the rolled material leaves the rolling mill and the upper and lower work rolls contact, so for example when the upper work roll is large sized and the lower work roll is not given a horizontal force imparting device, a difference will arise in the offset between the upper and lower work rolls and cause warping of the rolled material. In addition, there was the problem that a slight cross angle and thrust force are generated between the lower work roll and the lower backup roll and meandering and camber occur.
WO01/064360 discloses a rolling mill provided with a first pushing device giving a upper and lower direction balance force or bender force to the rolls through roll bearing boxes of the work rolls of the rolling mill and second pushing device giving a pushing force in a direction perpendicular to the rolling roll axis in the horizontal plane.
However, the external forces due to these pushing devices are given through the bearing boxes, so in the same way as Japanese Patent No. 2796465, there was the problem that it was not possible to suppress fluctuation in the work roll offset due to looseness of the work roll bearings present between the work roll bearing boxes and the work rolls.
Further, in a work roll driven four-stage rolling mill or six-stage rolling mill, to stabilize the positions of the work rolls in the horizontal plane, for example, in a hot rolling final rolling mill with work rolls of a diameter of 800 mm and backup rolls of a diameter of 1600 mm, the practice has been to set the rolling direction offset of the work roll axial center positions and the backup roll axial center positions to 6 to 13 mm or so, give the rolling load horizontal direction force component, that is, the offset force component, to the work rolls, and push the work roll chocks against the project blocks of the rolling mill housing or work roll chock support members connected to the backup roll chocks to stabilize the work roll position.
However, the offset force component is a force component of the rolling load, so is instantaneously applied when the rolled material is taken in. Therefore, there were the problems that a upper and lower and a left and right difference occurred in the work roll offset and led to warping of the rolled material or generation of a thrust force between the work rolls and backup rolls.